Glioblastoma multiforme (GBM) is a deadly and relatively common form of brain cancer. Despite poor prognoses, few meaningful treatment options are available to GBM patients. Treatment resistance and severe malignancy are driven in part by a subpopulation of stem cells that reside within the tumor termed glioblastoma stem cells (GSCs). The severe malignancy associated with GSCs is encouraged by the unique vascular niche in which they reside. The formation of the tumor niche is instigated by factors released by GSCs, and, in turn, cell-cell and cell-matrix interactions in the niche drive GSC growth and invasion. Recent evidence is beginning to emerge that activity-dependent mechanisms also perturb GSC properties. Yet, very little is still known about how electrical crosstalk within the tumor niche effects GSC malignant features and this proposal will address this substantial gap in knowledge. The first aim is to determine the intrinsic membrane properties and channels that are aberrantly expressed by GSCs. Using single-cell patch-clamping, electrophysiological signatures of individual dissociated GSCs will be characterized. These properties will be further correlated with membrane channel expression levels using single-cell RT-PCR to gain an understanding of the physiological differences between GSCs and neural cells and how these differences may respond to extrinsic network signals. The second Aim will address how surrounding neural activity affects these physiological features as well as growth and migration of GSCs. GSCs will be cocultured on organotypic brain slices to create an ex vivo model of the GSC-neuron interactive environment, and surrounding cortical areas will be stimulated or silenced using pharmacological or optogenetic modulation. Surrounding neural activity is likely to modulate GSC membrane properties and rates of proliferation and migration. This proposal will test a novel niche factor that likely plays an important role in tumor propagation, and these results may direct innovative therapeutic interventions for the treatment of GBM.